Mechanism of polycyclic aromatic hydrocarbons degradation in the rhizosphere of Phragmites australis: Organic acid co-metabolism, iron-driven, and microbial response

• Published in: Environmental pollution (1987) 2023-06, Vol.327, p.121608-121608, Article 121608
• Main Authors: Zhang, Ni-chen, A, Dan, Chao, Yuan-qing, Li, Hai-Yan, Li, Charles, Lin, Qing-qi, Li, Ya-ying, Qiu, Rong-liang
• Format: Article
• Language: English
• Subjects: Acids; Bacteria - metabolism; Biodegradation, Environmental; Co-metabolic degradation; Dioxygenases - metabolism; Iron - metabolism; Iron-driven; Microbial community; Organic Chemicals - metabolism; Poaceae - metabolism; Polycyclic aromatic hydrocarbons; Polycyclic Aromatic Hydrocarbons - analysis; Rhizosphere; Root organic exudates; Soil Microbiology; Soil Pollutants - metabolism
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2023.121608

Microbial co-metabolism is crucial for the efficient biodegradation of polycyclic aromatic hydrocarbons (PAHs); however, their intrinsic mechanisms remain unclear. To explore the co-metabolic degradation of PAHs, root organic acids (ROAs) (phenolic ROAs: caffeic acid [CA] and ferulic acid [FA]; non-phenolic ROAs: oxalic acid [OA]) were exogenously added as co-metabolic substrates under high (HFe) and low (LFe) iron levels in this study. The results demonstrated that more than 90% of PAHs were eliminated from the rhizosphere of Phragmites australis. OA can promote the enrichment of unrelated degrading bacteria and non-specific dioxygenases. FA with a monohydroxy structure can activate hydroxylase; however, it relies on phytosiderophores released by plants (such as OA) to adapt to stress. Therefore, non-specific co-metabolism occurred in these units. The best performance for PAH removal was observed in the HFe–CA unit because: (a) HFe concentrations enriched the Fe-reducing and denitrifying bacteria and promoted the rate-limiting degradation for PAHs as the enzyme cofactor; (b) CA with a dihydroxyl structure enriched the related degrading bacteria, stimulated specific dioxygenase, and activated Fe to concentrate around the rhizosphere simultaneously to perform the specific co-metabolism. Understanding the co-metabolic degradation of PAHs will help improve the efficacy of rhizosphere-mediated remediation. [Display omitted] •Total removal of PAHs in rhizosphere exceeded 90% during a 28-day experiment.•Different functional structures of root organic acids lead diverse removal pathways.•Caffeic acid as key root exudate accelerates PAH removal by special co-metabolism.•Caffeic acid activates Fe in rhizosphere in HFe-CA unit thus accelerating removal.